Up until now, there have been provided a wide variety of sound image localizing apparatuses, one typical example of which is disclosed in, for example, the Japanese Patent Publication No. 2741817 and shown in FIG. 19.
In the conventional sound image localizing apparatus, an A/D conversion unit 2110 is connected with a test sound source. A convolution operation unit 2120 includes a left-ear convolution operation unit (1) 2120L, and a right-ear convolution operation unit (r) 2120R. A two-channel D/A conversion unit 2130 is designed to convert signals respectively inputted from the left-ear convolution operation unit (1) 2120L and the right-ear convolution operation unit (r) 2120R, from digital format into analog format, and to respectively output signals thus converted to left-ear and right-ear portions of a headphone such as, for example, an ear-plug type headphone, an inner-earphone, or the like, not shown. A space impulse response storage unit 2150 and a headphone inverse impulse response storage unit 2160 serve as database for storing a predetermined set of filter coefficients (convolution data). The convolution operation unit 2120 is designed to selectively download appropriate filter coefficients from the convolution data stored in the space impulse response storage unit 2150 and the headphone inverse impulse response storage unit 2160. Data “Soil(t)” stored in the space impulse response storage unit 2150 indicates a left-ear i-th response in a median plane, data “Soir(t)” indicates a right-ear i-th response in the median plane, data “Sdil(t)” indicates a left-ear i-th response in direction d, and data “H−1i(t)” indicates a headphone inverse impulse response. The convolution operation unit 2120 can be selectively connected with and input signals from output sections of the AID conversion unit 2110 and a sound source storage unit 2140 by means of a switch 2170.
The conventional sound image localizing apparatus thus constructed can generate sound image signals, for example, two-channel sound signals, collectively constitute a sound image in a manner of convoluting the sound source signal with space impulse responses and headphone inverse impulse responses collectively corresponding to a direction to which the sound image is to be localized.
The conventional sound image localizing apparatus, however, encounters a drawback that the conventional sound image localizing apparatus is designed to store a set of typical filter coefficients. This leads to the fact that the space impulse responses, i.e., head-related impulse responses are required to be measured and generated for all the directions, to which the sound image is to be located, thereby requiring an enormous amount of laborious works and time for the measurement. Furthermore, the conventional sound image localizing apparatus requires a large amount of storage areas for storing the set of filter coefficients.
The conventional sound image localizing apparatus is operative to convolute the sound source signal with the headphone inverse impulse responses to suppress inverse characteristics inherent in the headphone. The conventional sound image localizing apparatus, however, cannot correct the variation of an ear canal transfer function resulted from a headphone or an earphone mounted on the listener's outer ear, thereby leading to the fact that the conventional sound image localizing apparatus cannot accurately localize a sound image when a headphone or an earphone is mounted on the listener's outer ear.
In view of the foregoing problems, it is an object of the present invention to provide a sound image localizing apparatus, which can accurately localize a sound image with a small amount of storage areas, as well as eliminate a need of measuring and generating head-related impulse responses for all the directions, to which the sound image is to be located.